A control device for an internal combustion engine in which an oxygen concentration sensor that is provided with a solid electrolyte body, an exhaust gas side electrode being disposed on one side of the solid electrolyte body and being in contact with the exhaust gas, a reference gas side electrode being disposed on the other side of the solid electrolyte body and being in contact with reference gas, and a diffusion velocity layer covering the exhaust gas side electrode is arranged in an engine exhaust passage and an air-fuel ratio is controlled based on an output of the oxygen concentration sensor is known (refer to Patent Literature 1). This oxygen concentration sensor generates an output voltage higher than a reference voltage corresponding to a theoretical air-fuel ratio when the air-fuel ratio is lower than the theoretical air-fuel ratio and generates an output voltage lower than the reference voltage when the air-fuel ratio is higher than the theoretical air-fuel ratio. Accordingly, it is determined that the air-fuel ratio is lower than the theoretical air-fuel ratio and the air-fuel ratio is controlled to be increased when the output voltage is higher than the reference voltage. It is determined that the air-fuel ratio is higher than the theoretical air-fuel ratio and the air-fuel ratio is controlled to be decreased when the output voltage is lower than the reference voltage. In this case, the diffusion velocity layer has the function of controlling the diffusion rate of the exhaust gas. In this oxygen concentration sensor, no voltage is applied between the exhaust gas side electrode and the reference gas side electrode.